Fate of N additions in a multiple resource‐limited Mediterranean oak savanna

Morris, Kendalynn; Nair, Richard; Moreno, Gerardo; Schrumpf, Marion; Migliavacca, Mirco

doi:10.1002/ecs2.2921

Cited by 7 publications

(7 citation statements)

References 69 publications

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“…At the end of February and early March 2016, a second dose of the same fertilizers was successively added into NT (20 kg N/ha) and NPT (10 kg P/ha and 20 kg N/ha), respectively. The total doses of N were approximately 10 times higher than the current N deposition rate in this area (Morris et al., 2019). The P addition in the NP site was calibrated to compensate for the N imbalance and maintain the original N:P stoichiometry of the ecosystem's herbaceous layer (Nair et al., 2019).…”

Section: Methodsmentioning

confidence: 77%

“…Few studies on nutrient and water interaction have been conducted in the semi‐arid tree–grass ecosystem (Nomura & Kikuzawa, 2003; Xia & Wan, 2013; Yin, Zheng, Cao, Song, & Yu, 2016). One particularly understudied system is located in Mediterranean climate zones, where typical tree–grass systems have complex structure and changing limiting resources throughout the year, with water limitations in the summer dry season, nutrient limitations in the rainy seasons (Moreno, 2008; Morris, Nair, Moreno, Schrumpf, & Migliavacca, 2019; Nair et al., 2019; Sardans & Peñuelas, 2013). These complex interactions imply that determining the interlinkage between nutrients (i.e., N and P) and water availability in shaping vegetation phenology and its activity in such ecosystems is a major challenge (Piao et al., 2019).…”

Section: Introductionmentioning

confidence: 99%

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Nutrients and water availability constrain the seasonality of vegetation activity in a Mediterranean ecosystem

Luo

El‐Madany

et al. 2020

Global Change Biology

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Anthropogenic nitrogen (N) deposition and resulting differences in ecosystem N and phosphorus (P) ratios are expected to impact photosynthetic capacity, that is, maximum gross primary productivity (GPPmax). However, the interplay between N and P availability with other critical resources on seasonal dynamics of ecosystem productivity remains largely unknown. In a Mediterranean tree–grass ecosystem, we established three landscape‐level (24 ha) nutrient addition treatments: N addition (NT), N and P addition (NPT), and a control site (CT). We analyzed the response of ecosystem to altered nutrient stoichiometry using eddy covariance fluxes measurements, satellite observations, and digital repeat photography. A set of metrics, including phenological transition dates (PTDs; timing of green‐up and dry‐down), slopes during green‐up and dry‐down period, and seasonal amplitude, were extracted from time series of GPPmax and used to represent the seasonality of vegetation activity. The seasonal amplitude of GPPmax was higher for NT and NPT than CT, which was attributed to changes in structure and physiology induced by fertilization. PTDs were mainly driven by rainfall and exhibited no significant differences among treatments during the green‐up period. Yet, both fertilized sites senesced earlier during the dry‐down period (17–19 days), which was more pronounced in the NT due to larger evapotranspiration and water usage. Fertilization also resulted in a faster increase in GPPmax during the green‐up period and a sharper decline in GPPmax during the dry‐down period, with less prominent decline response in NPT. Overall, we demonstrated seasonality of vegetation activity was altered after fertilization and the importance of nutrient–water interaction in such water‐limited ecosystems. With the projected warming‐drying trend, the positive effects of N fertilization induced by N deposition on GPPmax may be counteracted by an earlier and faster dry‐down in particular in areas where the N:P ratio increases, with potential impact on the carbon cycle of water‐limited ecosystems.

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Section: Methodsmentioning

confidence: 77%

Section: Introductionmentioning

confidence: 99%

Nutrients and water availability constrain the seasonality of vegetation activity in a Mediterranean ecosystem

Luo

El‐Madany

et al. 2020

Global Change Biology

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“…This was emphasized by the reduction of [N] during the experiment. Also, the highest N availability in the soil is expected to occur during the fall with the re‐wetting of the soil after the summer drought (Joffre, 1990; Morris et al., 2019). This increased N availability then caused a faster development of the vegetation biomass (Luo et al., 2020) and higher gross and net carbon uptake rates.…”

Section: Discussionmentioning

confidence: 99%

How Nitrogen and Phosphorus Availability Change Water Use Efficiency in a Mediterranean Savanna Ecosystem

et al. 2021

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Nutrient availability, especially of nitrogen (N) and phosphorus (P), is of major importance for every organism and at a larger scale for ecosystem functioning and productivity. Changes in nutrient availability and potential stoichiometric imbalance due to anthropogenic nitrogen deposition might lead to nutrient deficiency or alter ecosystem functioning in various ways. In this study, we present 6 years (2014–2020) of flux‐, plant‐, and remote sensing data from a large‐scale nutrient manipulation experiment conducted in a Mediterranean savanna‐type ecosystem with an emphasis on the effects of N and P treatments on ecosystem‐scale water‐use efficiency (WUE) and related mechanisms. Two plots were fertilized with N (NT, 16.9 Ha) and N + P (NPT, 21.5 Ha), and a third unfertilized plot served as a control (CT). Fertilization had a strong impact on leaf nutrient stoichiometry only within the herbaceous layer with increased leaf N in both fertilized treatments and increased leaf P in NPT. Following fertilization, WUE in NT and NPT increased during the peak of growing season. While gross primary productivity similarly increased in NT and NPT, transpiration and surface conductance increased more in NT than in NPT. The results show that the NPT plot with higher nutrient availability, but more balanced N:P leaf stoichiometry had the highest WUE. On average, higher N availability resulted in a 40% increased leaf area index (LAI) in both fertilized treatments in the spring. Increased LAI reduced aerodynamic conductance and thus evaporation at both fertilized plots in the spring. Despite reduced evaporation, annual evapotranspiration increased by 10% (48.6 ± 28.3 kg H2O m−2), in the NT plot, while NPT remained similar to CT (−1%, −6.7 ± 12.2 kgH2O m−2). Potential causes for increased transpiration at NT could be increased root biomass and thus higher water uptake or rhizosphere priming to increase P‐mobilization through microbes. The annual net ecosystem exchange shifted from a carbon source in CT (75.0 ± 20.6 gC m−2) to carbon‐neutral in both fertilized treatments [−7.0 ± 18.5 gC m−2 (NT) 0.4 ± 22.6 gC m−2 (NPT)]. Our results show, that the N:P stoichiometric imbalance, resulting from N addition (without P), increases the WUE less than the addition of N + P, due to the strong increase in transpiration at NT, which indicates the importance of a balanced N and P content for WUE.

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“…These added N to ES-LM1 (100 kg N ha -1 as Caammonium nitrate fertilizer) and N and P (an additional 50 kg P, as triple superphosphate fertilizer and N as ammonium nitrate) to ES-LM2. This load was equivalent to 10 years atmospheric N deposition (Morris et al, 2019), with P sufficient to maintain average ecosystem-scale leaf N:P ratios. A supplementary N and P fertilization was made in 2016/2017 adding 20% of the initial fertilization and a small extra P addition (6 kg ha-1) was made in the 2019 autumn to start a refertilization which was ultimately delayed by the coronavirus pandemic This design was informed by a small-scale fully factorial experiment showing N limitation at plot level, with a limited herbaceous response to P without N (Martini et al, 2019;Perez-Priego et al, 2015).…”

Section: Study Sitementioning

confidence: 99%

“…Hence aspects of the system are limited by P. These allometric shifts may alter C cycling and thus CUEECO through plant C investment to obtain N, P, or water. Microbial biomass also peaks in autumn, capitalizing on release from moisture restrictions (Morris et al, 2019). Overall C and water flux responses are discussed at length in El-Madany et al, (2021), here we focus specifically on CUEECO, and how this changes based on meteorological and vegetation conditions.…”

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confidence: 99%

Nitrogen Availability and Summer Drought, but not N:P Imbalance Drive Carbon Use Efficiency of a Mediterranean Tree-Grass Ecosystem

Nair,

Luo,

El-Madany

et al. 2023

Preprint

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Abstract. All ecosystems are simultaneously a source and a sink of atmospheric carbon (C). A change in their balance of net and gross ecosystem carbon uptake, ecosystem-scale carbon use efficiency (CUEECO), is a change in their ability to buffer climate change. Anthropogenic nitrogen (N) deposition is increasing N availability, potentially shifting terrestrial ecosystem stoichiometry towards phosphorus (P) limitation. Depending on how gross primary production (GPP, plants alone) and ecosystem respiration (RECO, plants and heterotrophs) are limited by N, P, or associated changes in other biogeochemical cycles, CUEECO may change. Seasonally, CUEECO also varies as GPP is more coupled to the growing season than respiration. We worked in a Mediterranean tree-grass ecosystem (locally called ‘dehesa’) characterized by mild, wet winters and summer droughts. We examined CUEECO from eddy covariance fluxes over six years under control, +N and +NP fertilized treatments on three timescales: annual, seasonal (determined by vegetation phenophase) and two-weekly aggregations. Finer aggregation allowed consideration of responses to specific vegetation and meteorological conditions. We predicted that CUEECO should be increased by wetter conditions, and by NP fertilization. Milder and wetter years with proportionally longer growing seasons increased CUEECO, as did N fertilization, regardless of whether P was added. Using a generalized additive model, whole ecosystem vegetation status and water deficit indicators, which both varied with treatment, were the main determinants of biweekly differences in CUEECO. The direction of water effects depended on the timescale considered and occurred alongside treatment-dependent water depletion.

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Fate of N additions in a multiple resource‐limited Mediterranean oak savanna

Cited by 7 publications

References 69 publications

Nutrients and water availability constrain the seasonality of vegetation activity in a Mediterranean ecosystem

Nutrients and water availability constrain the seasonality of vegetation activity in a Mediterranean ecosystem

How Nitrogen and Phosphorus Availability Change Water Use Efficiency in a Mediterranean Savanna Ecosystem

Nitrogen Availability and Summer Drought, but not N:P Imbalance Drive Carbon Use Efficiency of a Mediterranean Tree-Grass Ecosystem

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